This invention concerns a compact four-cycle internal combustion engine according to the preamble of claim 1.
Such an engine which works with a mixture lubrication and which is appropriate in particular for being used in a portable working device, for example a motor scythe or a motor saw, is known from the printed document DE-A1-42 20 200.
From the prior art, we know a four-cycle internal combustion engine with oil lubrication, the oil being separately stored from the fuel. The oil is purposefully delivered to the corresponding lubrication points, or it comes from an oil sump as an oil-air mixture (oil mist) to the lubrication points.
An engine lubrication with a fuel-oil-air mixture, similar to the lubrication of two-cycle engines, is also known. The fuel-oil-air mixture is preliminarily stored in the crankcase and supplied to the rotary valve inlet over a duct. A flowing back of the mixture into the carburetor is avoided by a diaphragm valve (see the printed document DE-A1-42 20 200 mentioned in the introduction).
A disadvantage of such a rotary valve controlled lubrication system is that the whole fuel-oil-air mixture flows over a relatively long path through the crankcase, although only a comparatively slight part of the mixture is required for the lubrication in the area of the crankcase. But it is also disadvantageous that an additional valve mechanism must be provided between the crankcase and the carburetor, whereby this mechanism causes an increasement of costs and can be, as an additional functional element, a further source of trouble during the operation.
Thus, the aim of the invention is to create a compact four-cycle internal combustion engine with rotary valve control and mixture lubrication which is characterized by a simplified assembly and which, due to an improved lubrication, allows in particular an operation independently from the position.
This aim is achieved by the whole characteristics of claim 1. The heart of the invention consists in the control not only of the filling and discharging of the combustion chamber but also in the guiding of a part of the mixture temporarily into the combined cylinder/crankcase chamber and then in the flowing back again out of the cylinder/crankcase chamber for filling the combustion chamber. The combustion chamber is filled mainly directly by the mixture coming from the carburetor. The additional mixture coming from the crankcase chamber assists the filling. Thus, it is possible to guarantee an adapted position independent lubrication simultaneously with a compact assembly and short duct ways. Moreover, a recharging effect is achieved by the additionally supplied mixture from the crankcase chamber.
The assembly is particularly space saving when, according to a preferred embodiment of the invention, the rotary valve is placed in the cylinder head and when the rotary valve is driven by the crankshaft over a gear which preferably comprises two toothed wheels and a toothed belt.
Preferably, the rotary valve comprises a cylindrical body in which two channels and a recess are provided for realizing the connections. The channels can also be realized as a recess and the recess as channels. The body is not necessarily cylindrical, other forms such as balls or crowned bodies are also possible.